Assuming I'm willing to pull out all the stops, what is the best wine to use in a "standard" gruyere-based fondue, like this one?
Any white with a sufficiently high acid content. The canonical fondue wine is Fendant, which is made in the valais region out of chasselas grapes, so any chasselas (see Wikipedia for a long list of alternative names) will work well.
One notable alternative is a dry champagne. This will make your fondue very light and fluffy, due to the carbonation.